The process of this invention relates to a process for the preparation of phenolphthalein from phthalic anhydride and phenol in the presence of acid form cation exchange resins and aryl phosphites.
The use of Friedel-Crafts condensing agents such as, zinc chloride, tin chloride, sulfuric acid, benzene sulfonic acid and mixtures thereof is well known in the art for this condensation reaction as is illustrated by U.S. Pat. Nos. 1,381,503; 1,940,494; 1,995,402; 2,168,346; 2,192,485; 2,522,939; and 2,522,940.
Sollazzo, et al. in La Chemica L'Industria 38:509 (1956) showed that a mixture of zinc chloride and Amberlite IR 120 (a sulfonic cation exchange resin) could be used as a combined condensing agent to produce phenolphthalein.
It has been reported by Bilik, et al. Chemical Abstracts 70:96355 (1969) that sulfonic cation exchange resins alone can be used as a catalyst in the reaction. However, Bilik, et al. found the reaction to be very slow and gave poor yields, i.e., 40 hours reaction time and 18.6% yield.
In Ser. No. 750,786 filed Dec. 15, 1976, a process is disclosed wherein a cation exchange resin is used in conjunction with azeotropic distillation to produce phenolphthalein.